Well, as for rivalries, there are of course many. And all are rooted deply in fan enthusiasm and tradition. But there is only one rivalry where the participants all have to wear protective gear, including the fans.
Any Raiders/Chargers matchup. It's become so dangerous, that San Diego has now implemented the ticket program where fans have to purchase at least 2 more Charger home game tickets to go to one game. That is esigned to discourage the Raider fans from LA and Oakland from buying all the tickets. They still find ways to get there, but not near as many.
At least 100 get arrested during the game for fighting every time these 2 teams play in SD. It's dangerous.